Date: Wed, 18 Sep 2002 18:31:54 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Alfred Perlstein <alfred@FreeBSD.org> Cc: hackers@freebsd.org, deischen@freebsd.org, Garrett Wollman <wollman@lcs.mit.edu> Subject: Re: sem_init help? Message-ID: <3D89290A.B05D1882@mindspring.com> References: <20020919005959.GO86737@elvis.mu.org>
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Alfred Perlstein wrote: > Ok, any of you guys have a copy of the standards documents that > describe the sem_* API? > > I have a question... > > What are the semantics of the sem_init when pshared is set to true? The sem_init() function is used to initialise the unnamed semaphore referred to by sem. The value of the initialised semaphore is value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(), sem_trywait(), sem_post(), and sem_destroy(). This semaphore remains usable until the semaphore is destroyed. If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the semaphore sem can use sem for performing sem_wait(), sem_trywait(), sem_post(), and sem_destroy() operations. Only sem itself may be used for performing synchronisation. The result of referring to copies of sem in calls to sem_wait(), sem_trywait(), sem_post(), and sem_destroy(), is undefined. If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this process can use sem for performing sem_wait(), sem_trywait(), sem_post(), and sem_destroy() operations. The use of the semaphore by threads other than those created in the same process is undefined. Attempting to initialise an already initialised semaphore results in undefined behaviour. > Like, if the process that created the semaphore exits, then what? The use of the semaphore by threads other than those created in the same process is undefined. > Is it only valid for the life of the process that did the sem_init? The use of the semaphore by threads other than those created in the same process is undefined. 8-). -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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